Terrestrial Trunk Radio (TETRA) is a global standard for radio communications on mobile communication devices, such as private/professional mobile radios (herein simply referred to as radios). Any TETRA standards or specifications referred to herein may be obtained by contacting ETSI at ETSI Secretariat, 650, Route des Lucioles, 06921 Sophia-Antipolis Cedex, FRANCE. Professional mobile radios include radios, other than mobile telephones, such as mobile radios, portable radios, and the like. A TETRA network coverage area is configured to include a predefined geographical area. Currently there are a large number of TETRA systems for private companies, as well as, TETRA systems for nation wide public service organizations. These systems are typically separate so that radios assigned to one system may only communicate with other radios in that system. For a radio to communicate in each TETRA system, the radio keeps track of a unique Individual Short Subscriber Identity (ISSI) assigned to each of the other radios in the specific system in which the radio operates. Each radio typically maintains an address book (herein referred to as a home address book), wherein device information in the home address book is associated with the corresponding radio ISSI. The address book is typically stored in digital format in a memory device and the address book may include information associated with each radio in the TETRA system. When a radio receives a call (a communication signal sent from another radio according to a communication protocol), the radio uses the calling radio's ISSI to retrieve information, such as contact information, associated with the calling radio from the home address book. In order to place a call to another radio, the calling radio also uses the home address book to find the ISSI associated with the radio to be called. It should be noted that the home address book may also include the Individual TETRA Subscriber Identity (ITSI) to be used instead of the ISSI.
Selected radios may be able to migrate between separate TETRA systems, which means that they are allowed to roam between separate TETRA systems, for example to cooperate with other radios in border areas. The ISSI of a selected radio (a migrating radio that is allowed to migrate from a home TETRA system to a visited TETRA system) may be coordinated with the ISSIs assigned to radios in the visited TETRA system so that the ISSI for the migrating radio remains unique to the migrating radio in the visited TETRA system as well as in the home TETRA system. However, because ISSIs assigned to other radios in the visited and home TETRA systems are only coordinated based on the ISSI for the migrating radio, the same ISSI may be used by a non-migrating radio in the home TETRA system and another non-migrating radio in the visited TETRA system. Accordingly, when the migrating radio receives a call from a radio in the visited TETRA system, if the calling radio in the visited TETRA system is assigned the same ISSI as another radio in the home TETRA system, the migrating radio will use that ISSI to retrieve a caller identifier (ID) for the calling radio from its home address book. Because the migrating radio's address book is associated with radios in its home TETRA system, the migrating radio will erroneously display or otherwise present the contact information associated with the radio in its home system, rather than the contact information associated with the radio in the visited TETRA system. Similarly, when two radios are assigned the same ISSI, the migrating radio may erroneously direct a call to the wrong radio.
Users are typically grouped into logical talk groups to facilitate group discussion where users on different radios cooperate. In some situations, it may be essential for a group participant to join a group call. In TETRA systems, each group is assigned a Group Short Subscriber Identity (GSSI) or a Group TETRA Subscriber Identity (GTSI). According to the TETRA standards, groups may be group-linked. For example, a group five (5) in the home TETRA system may be linked to a group ten (10) in the visited TETRA system. When the migrating radio migrates to the visited TETRA system, the migrating radio remains linked to the group in its home TETRA system. The migrating radio is not configured to automatically link to the correct group in the visited TETRA system.
Accordingly, there is a need for a method and apparatus for enabling a migrating radio to dynamically switch its operating address book upon roaming to a visited TETRA system.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.